This invention relates generally to the art of electrochromic cells, and more particularly to the art of transparent electrochromic devices comprising plastic substrates.
Conventional electrochromic cells comprise a thin film of a persistent electrochromic material, i.e. a material responsive to the application of an electric field of a given polarity to change from a high-transmittance, non-absorbing state to a lower-transmittance, absorbing or reflecting state and remaining in the lower-transmittance state after the electric field is discontinued, preferably until an electric field of reversed polarity is applied to return the material to the high-transmittance state. The electrochromic film, which is both an ionic and electronic conductor, is in ion-conductive contact, preferably direct physical contact, with a layer of ion-conductive material. The ion-conductive material may be solid, liquid or gel, but is preferably a polymer layer. The electrochromic film and ion-conductive layers are disposed between two electrodes.
As a voltage is applied across the two electrodes, ions are conducted through the ion-conducting layer. When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of the film. Reversing the polarity causes reversal of the electrochromic properties, and the film reverts to its high transmittance state. Typically, the electrochromic film, preferably tungsten oxide, is deposited on a glass substrate coated with an electroconductive film such as tin oxide to form one electrode. The counter electrode has typically been a carbon-paper structure backed by a similar tin oxide coated glass substrate or a metal plate.
U.S. Pat. No. 4,174,152 to Giglia et al. discloses electrochromic devices wherein the polymeric electrolyte material is a hydrophilic copolymer of a selected acrylate or methacrylate monomer and a selected acid group containing monomer, e.g. 2-acrylamido-2-methylpropanesulfonic acid.
U.S. Pat. No. 4,335,938 to Giglia discloses electrochromic devices having a layer of tungsten oxide in contact with a layer of organic electrolyte resin comprising a hydrophilic layer of homopolymer of poly(2-acrylamido-2-methylpropanesulfonic acid) with electrode means for changing electrochromic properties of the device. A conventional electrochromic device is described as having a transparent electrochromic electrode comprising a glass substrate with a conductive tin oxide layer and an electrochromic, e.g. tungsten oxide, film; a pigmented, ion-conducting medium layer comprising a self-supporting layer of ion-conductive polymer having a pigment dispersed therein; and an opaque counter electrode such as carbon paper.
U.S. Pat. Nos. 4,361,385 and 4,478,991 to Huang et al. disclose electrochromic devices having a layer of electrochromic tungsten oxide in contact with a polymeric electrolyte wherein the stability and speed of the device are improved by using a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and vinyl sulfonic acid as the polymer electrolyte. An electrochromic film on an electrode is prepared by evaporation of an amorphous film of tungsten oxide onto a glass substrate coated with conductive tin oxide. The polymer mixture is cast, dried and hydrated in contact with the electrochromic film, and then a second electrode consisting of paper-carbon is pressed against the polymer layer with a second tin oxide coated glass plate backing the carbon-paper electrode.
U.S. Pat. Nos. 4,554,318; 4,609,703 and 4,670,350 to Rukavina disclose novel copolymers of acrylic acid and cyanoethylacrylate, including terpolymers with hydroxyethylacrylate, useful as primers for bonding metal-containing coatings to organic polymer substrates.
Cogan et al. describe electrochromic devices in SPIE, Vol. 823, No. 482 (1987) comprising indium/tin oxide (ITO) coated glass electrodes, electrochromic films of tungsten oxide and iridium oxide, and a polymer electrolyte of acrylamidopropanesulfonic acid (AMPS).